Feshbach resonances with large background scattering length: interplay with open-channel resonances

Feshbach resonances are commonly described by a single-resonance Feshbach model, and open-channel resonances are not taken into account explicitly. However, an open-channel resonance near threshold limits the range of validity of this model. Such a situation exists when the background scattering length is much larger than the range of the interatomic potential. The open-channel resonance introduces strong threshold effects not included in the single-resonance description. We derive an easy-to-use analytical model that takes into account both the Feshbach resonance and the open-channel resonance. We apply our model to $^{85}$Rb, which has a large background scattering length, and show that the agreement with coupled-channels calculations is excellent. The model can be readily applied to other atomic systems with a large background scattering length, such as $^6$Li and $^{133}$Cs. Our approach provides full insight into the underlying physics of the interplay between open-channel (or potential) resonances and Feshbach resonances.Comment: 16 pages, 12 figures, accepted for publication in Phys. Rev. A; v2: added reference

Far infrared CO and H2_2O emission in intermediate-mass protostars

Intermediate-mass young stellar objects (YSOs) provide a link to understand how feedback from shocks and UV radiation scales from low to high-mass star forming regions. Aims: Our aim is to analyze excitation of CO and H$_2$O in deeply-embedded intermediate-mass YSOs and compare with low-mass and high-mass YSOs. Methods: Herschel/PACS spectral maps are analyzed for 6 YSOs with bolometric luminosities of $L_\mathrm{bol}\sim10^2 - 10^3$ $L_\odot$. The maps cover spatial scales of $\sim 10^4$ AU in several CO and H$_2$O lines located in the $\sim55-210$ $\mu$m range. Results: Rotational diagrams of CO show two temperature components at $T_\mathrm{rot}\sim320$ K and $T_\mathrm{rot}\sim700-800$ K, comparable to low- and high-mass protostars probed at similar spatial scales. The diagrams for H$_2$O show a single component at $T_\mathrm{rot}\sim130$ K, as seen in low-mass protostars, and about $100$ K lower than in high-mass protostars. Since the uncertainties in $T_\mathrm{rot}$ are of the same order as the difference between the intermediate and high-mass protostars, we cannot conclude whether the change in rotational temperature occurs at a specific luminosity, or whether the change is more gradual from low- to high-mass YSOs. Conclusions: Molecular excitation in intermediate-mass protostars is comparable to the central $10^{3}$ AU of low-mass protostars and consistent within the uncertainties with the high-mass protostars probed at $3\cdot10^{3}$ AU scales, suggesting similar shock conditions in all those sources.Comment: Accepted to Astronomy & Astrophysics. 4 pages, 5 figures, 3 table

Testing particle trapping in transition disks with ALMA

We present new Atacama Large Millimeter/submillimeter Array (ALMA) continuum observations at 336GHz of two transition disks, SR21 and HD135344B. In combination with previous ALMA observations from Cycle 0 at 689GHz, we compare the visibility profiles at the two frequencies and calculate the spectral index ($\alpha_{\rm{mm}}$). The observations of SR21 show a clear shift in the visibility nulls, indicating radial variations of the inner edge of the cavity at the two wavelengths. Notable radial variations of the spectral index are also detected for SR21 with values of $\alpha_{\rm{mm}}{\sim}3.8-4.2$ in the inner region ($r<35$ AU) and $\alpha_{\rm{mm}}{\sim}2.6-3.0$ outside. An axisymmetric ring (which we call the ring model) or a ring with the addition of an azimuthal Gaussian profile, for mimicking a vortex structure (which we call the vortex model), is assumed for fitting the disk morphology. For SR21, the ring model better fits the emission at 336GHz, conversely the vortex model better fits the 689GHz emission. For HD135344B, neither a significant shift in the null of the visibilities nor radial variations of $\alpha_{\rm{mm}}$ are detected. Furthermore, for HD135344B, the vortex model fits both frequencies better than the ring model. However, the azimuthal extent of the vortex increases with wavelength, contrary to model predictions for particle trapping by anticyclonic vortices. For both disks, the azimuthal variations of $\alpha_{\rm{mm}}$ remain uncertain to confirm azimuthal trapping. The comparison of the current data with a generic model of dust evolution that includes planet-disk interaction suggests that particles in the outer disk of SR21 have grown to millimetre sizes and have accumulated in a radial pressure bump, whereas with the current resolution there is not clear evidence of radial trapping in HD135344B, although it cannot be excluded either.Comment: Minor changes after language edition. Accepted for publication in A&A (abstract slightly shortened for arXiv

Radio-Frequency Spectroscopy of Ultracold Fermions

Radio-frequency techniques were used to study ultracold fermions. We observed the absence of mean-field "clock" shifts, the dominant source of systematic error in current atomic clocks based on bosonic atoms. This is a direct consequence of fermionic antisymmetry. Resonance shifts proportional to interaction strengths were observed in a three-level system. However, in the strongly interacting regime, these shifts became very small, reflecting the quantum unitarity limit and many-body effects. This insight into an interacting Fermi gas is relevant for the quest to observe superfluidity in this system.Comment: 6 pages, 6 figure

Dust, Ice and Gas in Time (DIGIT) Herschel program first results: A full PACS-SED scan of the gas line emission in protostar DK Cha

DK Cha is an intermediate-mass star in transition from an embedded configuration to a star plus disk stage. We aim to study the composition and energetics of the circumstellar material during this pivotal stage. Using the Range Scan mode of PACS on the Herschel Space Observatory, we obtained a spectrum of DK Cha from 55 to 210 micron as part of the DIGIT Key Program. Almost 50 molecular and atomic lines were detected, many more than the 7 lines detected in ISO-LWS. Nearly the entire ladder of CO from J=14-13 to 38-37 (E_u/k = 4080 K), water from levels as excited as E_u/k = 843 K, and OH lines up to E_u/k = 290 K were detected. The continuum emission in our PACS SED scan matches the flux expected from a model consisting of a star, a surrounding disk of 0.03 Solar mass, and an envelope of a similar mass, supporting the suggestion that the object is emerging from its main accretion stage. Molecular, atomic, and ionic emission lines in the far-infrared reveal the outflow's influence on the envelope. The inferred hot gas can be photon-heated, but some emission could be due to C-shocks in the walls of the outflow cavity.Comment: 4 Page letter, To appear in A&A special issue on Hersche

Predicting scattering properties of ultracold atoms: adiabatic accumulated phase method and mass scaling

Ultracold atoms are increasingly used for high precision experiments that can be utilized to extract accurate scattering properties. This calls for a stronger need to improve on the accuracy of interatomic potentials, and in particular the usually rather inaccurate inner-range potentials. A boundary condition for this inner range can be conveniently given via the accumulated phase method. However, in this approach one should satisfy two conditions, which are in principle conflicting, and the validity of these approximations comes under stress when higher precision is required. We show that a better compromise between the two is possible by allowing for an adiabatic change of the hyperfine mixing of singlet and triplet states for interatomic distances smaller than the separation radius. A mass scaling approach to relate accumulated phase parameters in a combined analysis of isotopically related atom pairs is described in detail and its accuracy is estimated, taking into account both Born-Oppenheimer and WKB breakdown. We demonstrate how numbers of singlet and triplet bound states follow from the mass scaling.Comment: 14 pages, 9 figure

Uncertainty-principle noise in vacuum-tunneling transducers

The fundamental sources of noise in a vacuum-tunneling probe used as an electromechanical transducer to monitor the location of a test mass are examined using a first-quantization formalism. We show that a tunneling transducer enforces the Heisenberg uncertainty principle for the position and momentum of a test mass monitored by the transducer through the presence of two sources of noise: the shot noise of the tunneling current and the momentum fluctuations transferred by the tunneling electrons to the test mass. We analyze a number of cases including symmetric and asymmetric rectangular potential barriers and a barrier in which there is a constant electric field. Practical configurations for reaching the quantum limit in measurements of the position of macroscopic bodies with such a class of transducers are studied

Herschel observations of the hydroxyl radical (OH) in young stellar objects

Water in Star-forming regions with Herschel (WISH) is a Herschel Key Program investigating the water chemistry in young stellar objects (YSOs) during protostellar evolution. Hydroxyl (OH) is one of the reactants in the chemical network most closely linked to the formation and destruction of H2O. High-temperature chemistry connects OH and H2O through the OH + H2 H2O + H reactions. Formation of H2O from OH is efficient in the high-temperature regime found in shocks and the innermost part of protostellar envelopes. Moreover, in the presence of UV photons, OH can be produced from the photo-dissociation of H2O. High-resolution spectroscopy of the OH 163.12 micron triplet towards HH 46 and NGC 1333 IRAS 2A was carried out with the Heterodyne Instrument for the Far Infrared (HIFI) on board Herschel. The low- and intermediate-mass YSOs HH 46, TMR 1, IRAS 15398-3359, DK Cha, NGC 7129 FIRS 2, and NGC 1333 IRAS 2A were observed with the Photodetector Array Camera and Spectrometer (PACS) in four transitions of OH and two [OI] lines. The OH transitions at 79, 84, 119, and 163 micron and [OI] emission at 63 and 145 micron were detected with PACS towards the class I low-mass YSOs as well as the intermediate-mass and class I Herbig Ae sources. No OH emission was detected from the class 0 YSO NGC 1333 IRAS 2A, though the 119 micron was detected in absorption. With HIFI, the 163.12 micron was not detected from HH 46 and only tentatively detected from NGC 1333 IRAS 2A. The combination of the PACS and HIFI results for HH 46 constrains the line width (FWHM > 11 km/s) and indicates that the OH emission likely originates from shocked gas. This scenario is supported by trends of the OH flux increasing with the [OI] flux and the bolometric luminosity. Similar OH line ratios for most sources suggest that OH has comparable excitation temperatures despite the different physical properties of the sources.Comment: Accepted for publication in Astronomy and Astrophysics (Herschel special issue

Quantum interference structures in the conductance plateaus of gold nanojunctions

The conductance of breaking metallic nanojunctions shows plateaus alternated with sudden jumps, corresponding to the stretching of stable atomic configurations and atomic rearrangements, respectively. We investigate the structure of the conductance plateaus both by measuring the voltage dependence of the plateaus' slope on individual junctions and by a detailed statistical analysis on a large amount of contacts. Though the atomic discreteness of the junction plays a fundamental role in the evolution of the conductance, we find that the fine structure of the conductance plateaus is determined by quantum interference phenomenon to a great extent.Comment: 4 pages, 4 figure